ABSTRACT
ABSTRACT Abiotic stress adversely limits plant growth and affects the world’s agriculture, while adaption to environmental stress factors is crucial for plant survival. Under both biotic and abiotic stress conditions, plants are forced to develop many enzymatic and nonenzymatic mechanisms in order to resist the production of toxic free radicals and enhance their defense systems. This chapter summarizes the melatonin-induced mechanisms of plant adaption under stress conditions such as heat, chilling, drought, salinity, irradiation, herbicides, heavy metals, pathogens, and senescence. Thus, exogenously applied melatonin may inuence plant adaptation to stress by (a) upregulating physiological parameters like water, monitoring concentrations of inorganic elements, enhancing ion homeostasis and chlorophyll content, improving photosynthetic efciency, maintaining cell turgor and membrane selectivity, accumulating net solutes, and acting as an osmoprotectant; (b) scavenging reactive oxygen species by reducing membrane damage, maintaining intracellular H2O2 concentrations, and keeping the oxidation-reduction system at steady, safe levels through an enzymatic or nonenzymatic mechanism; (c) regulating the phenylpropanoid pathway, stimulating the production of antioxidant compounds; (d) improving the activity of some stress-related enzymes; and (e) altering the expression of stress-response genes involved in all steps along the way from receptors through transcription factors.
